As evidenced by other patents and work over the last years, much effort has been put into creating fins with low drag, and powering systems that are as cost and energy efficient as possible. The art of reducing the unpleasant and at times dangerous roll motion of boats and ships in waves have evolved over many years, and there are many principle technologies used with varying benefits and results for different conditions, type of watercraft and not least cost of implementation and operation. Such different systems include fin stabilizers, gyro stabilizers and bilge tanks to mention the most common ones.
The traditional stabilization systems used in passenger vessels, naval vessels etc., were generally designed for use in underway situations and mostly for boats cruising in displacement mode and thereby in relatively low velocities. The watercrafts that have traditionally been using stabilizers, have also by their size and hull shapes generally had long roll times, thereby requiring relatively slow acting stabilization system, where counter forces are applied to the waves forces over relatively long time periods. Over the last 15 years, the market has evolved to a require roll stabilization when the watercraft is at anchor, i.e. not having any forward motion, as well as stabilization systems being installed in much faster boats, including planning boats. These changes create many new challenges and issues, as explained below.
One such known issue known issues is that with the watercraft not moving forward through the water, thus being able to make use of the forces in the waterflow passing the fins by the forward motion of the vessel to create a force to counter the waves forces that rolls the watercraft, the only way a fin stabilizer can apply a counter force, is to flap or swim the fins. This means that both the peak force possible as well as the time such a force can be applied is limited. The force is a result of the size of fin and the speed the fin is moved, and as an opposite, the faster the fin is moved, the shorter a time period the force can be applied as there is a limited physical movement of the fin, and it also has to be stopped without causing too much counter force in the undesired direction at the time. Mathematically, or as a term in physics, the total force impulse is in principal determined by the fin size.
A second issue, is the fact that modern faster watercrafts have a hull shape and a weight that makes their natural roll periods a lot shorter than the traditional vessels where stabilizers have been installed, and also that their physical requirement for stabilizer force is higher compared to the boat size in comparison with the traditional watercraft equipped with stabilizers. The principal mathematical way to calculate the necessary force of a stabilizing system to reduce the roll by a desired amount is mostly based on a factor called Metacentric height (GM). This is a factor decided by how stiff the watercraft is on the water, i.e. the more it follows the waves angles, the more force is required from the stabilizer system to counter this roll, and what a stabilizer system actually does, is to force the boat to not follow the waves angle.
Given the fact that these modern vessels both require more force, while also allowing a shorter period to apply this force, it is apparent that these vessels are much more difficult to stabilize.
The simple solution is to install very big fins to be able to reach the desired roll reduction force.
However, an issue that evidently has not been considered sufficiently, but is an important benefit in this invention, is that by using very large traditional fins to reach the desired roll reduction forces, this will also have other impacts on the vessels, the faster and lighter the watercraft, the more negative these impacts become. E.g., for a watercraft having 6 degrees of motion freedom in water, simply increasing the traditional force impulse will cause other negative effects on the watercraft by causing increased sway and yaw, both in underway and in at anchor situations. These effects are different from roll effects, but still uncomfortable and with negative effects on the boat.
At present, the overall market view is that fin stabilizers, even with the limitations of the present fins, provide the overall best solutions as a single technology system to use for both underway and at anchor stabilization, since most other solutions, like gyros or stabilization tanks, do not perform very well in underway situation of faster vessels. However, the problem of being able to apply enough force in at anchor situation, or at high speed with light weight vessels, without causing too many other negative implications on the watercraft, in general still remains to be solved for fin stabilizers.
One solution to improve this situation is presented in patent US 2007 0272143 and EP 1 577 210 that describes stabilizer fins that have the ability to change its size and shape, to thereby have different size in underway and at anchor situations, increasing the possible force without causing additional drag when not needed.
European patent application EP1577210 A1, describes an active roll stabilization system comprising fins with sub-elements, where the sub elements are movable, i.e. linked with respect to the fins.
One of the problems with prior art technology is that active roll stabilizers may cause the watercraft to sway or yaw due to the large forces applied on the stabilizers, and thereby creates another unpleasant movement for the passengers.
International application WO2014/065672 A1 discloses a curved stabilizer fin that improves the anti-roll efficiency of the fin and thereby also reduces the negative impact the fin movement has on the boat.
GB 2530550 A shows a pivoting flap that may be spring loaded.
GB 969 469 A discloses an arrangement for stabilizing ships, where lateral extending fins are rotated about an axis transverse to the direction of travel to reduce fin friction.
However, a major problem related to at anchor stabilization with fins rotating about a rotational axis connecting the fin to the hull, is that the paddling motion creates a forward directed force, trying to move the boat in a forward direction. When the boat is at anchor with an anchor line in the bow, the anchor line will prevent the boat from moving forward, and instead the boat will turn around. Eventually, the boats baseline will become parallel to the wave front, and the roll movement will increase. Thus, the advantages of the anti-roll system is actually reduced by the forces set up by the anti-roll system itself.